1. Field of the Invention
The present invention relates to a system for concurrently carrying out distillation or chemical reactions and separating the reactants and products by fractional distillation.
2. Related Art
A method of carrying out catalytic reactions has been developed and widely commercialized, wherein the components of the reaction mixture are concurrently separable by fractional distillation. Several systems have been proposed and one commercially successful system uses the catalyst as the catalytic distillation structure. Such a system is variously described in U.S. Pat. Nos. 4,215,011; 4,232,177; 4,242,530; 4,250,052; 4,302,356; 4,307,254; 4,336,407; 4,439,350; 4,443,559; and 4,482,775 commonly assigned herewith.
Briefly, the commercial catalytic structure described therein comprises a cloth belt with a plurality of pockets spaced along the belt and containing particulate catalyst material. The cloth belt with catalyst filled pockets is wound into a helix about a spacing material such as knitted stainless steel wire mesh, and these “bales” loaded into a distillation column. Additionally U.S. Pat. Nos. 4,302,356, 4,443,559 and 4,250,052 disclose a variety of catalyst structures for this use.
Placing the particulate catalyst loose on standard distillation trays has also been proposed. See, for example, U.S. Pat. No. 4,215,011 and U.K. patents GB 2,096,603 and 2,096,604. U.S. Pat. No. 4,439,350 discloses a clip which holds and supports closed porous containers of catalyst spaced apart from each other on a distillation tray within the liquid on the tray. The placement of the catalyst in the downcomers of standard distillation columns has been proposed as in U.S. Pat. No. 3,634,534. Fluidization of the catalyst on the trays has also been suggested as in U.S. Pat. No. 4,471,154. Some deficiencies of such fluidized beds were recognized in Chemiker Zeitung/Chemische Apparatur, vol. 90, no. 13, July 1966 and U.S. Pat. No. 4,215,011. Quang, et al, in U.S. Pat. No. 4,847,430 and Nocca, et al in U.S. Pat. No. 4,847,431 disclose loading the particulate catalyst on alternating trays of a distillation column and with a gas bypass about the catalyst loaded trays. The use of solid glass beads to disperse and support a catalyst in a fixed bed has long been used, especially in pilot plants and bench scale reactors. See for example U.S. Pat. No. 4,918,244 wherein glass beads were used as a dispersant and support in a bench scale reactor distillation column. So far, one of the most commercially successful arrangements has been to the place the particulate catalyst in closed pockets disposed along a fiber glass cloth belt as disclosed in U.S. Pat. No. 4,215,011.
The main problems sought to be overcome by the improvements have been the reduction of pressure drop through the column and provision of sufficient contact of the reactants with the catalyst while providing for good vapor liquid contact for the fractional distillation. Many useful catalysts are in the form of fine particulate powders which preclude their use directly as distillation components. Even larger extruded pellets do not lend themselves well as distillation structures. Hence the use of cloth belts, cages and support trays is the predominant developmental thrust. While larger catalysts structures have been proposed, the porosity requirements of many catalytic materials limit their structural integrity. Many catalysts which rely on outer surface activity only and which might have the strength for larger structures are useful only for gas phase reactions, such as maleic anhydride production. U.S. Pat. Nos. 4,443,559 and 5,266,546 both disclose catalytic distillation structures that may be placed on trays similar to sieve trays for support in a distillation column reactor.
The present invention is related to these structures and catalytic distillation, but it is also related to distillation in general. It is an advantage of the present invention that greater tower efficiency may be obtained for conventional distillation trays by use of the present system. No art is known to suggest the present invention and in fact conventional knowledge would suggest the present invention would be counterproductive. The unexpected benefit of the present invention will be obvious from the disclosures herein.